Efficient Density Matrix Renormalization Group algorithm to study Y-Junctions with integer and half-integer spin

Abstract

An efficient density matrix renormalization group (DMRG) algorithm is presented and applied to Y-junctions, systems with three arms of $n$ sites that meet at a central site. The accuracy is comparable to DMRG of chains. As in chains, new sites are always bonded to the most recently added sites and the superblock Hamiltonian contains only new or once renormalized operators. Junctions of up to $N=3n+1\approx 500$ sites are studied with antiferromagnetic (AF) Heisenberg exchange $J$ between nearest-neighbor spins $S$ or electron transfer $t$ between nearest neighbors in half-filled Hubbard models. Exchange or electron transfer is exclusively between sites in two sublattices with $N_A\ne N_B$. The ground state (GS) and spin densities ${\rho }_r=<S_r^z>$ at site $r$ are quite different for junctions with $S$ = 1/2, 1, 3/2 and 2. The GS has finite total spin $S_G=2S(S)$ for even (odd) $N$ and for $M_G=S_G$ in the $S_G$ spin manifold, ${\rho }_r>0(<0)$ at sites of the larger (smaller) sublattice. $S$ = 1/2 junctions have delocalized states and decreasing spin densities with increasing $N$. $S$ = 1 junctions have four localized $S_z=1/2$ states at the end of each arm and centered on the junction, consistent with localized states in $S$ = 1 chains with finite Haldane gap. The GS of $S$ = 3/2 or 2 junctions of up to 500 spins is a spin density wave (SDW) with increased amplitude at the ends of arms or near the junction. Quantum fluctuations completely suppress AF order in $S$ = 1/2 or 1 junctions, as well as in half-filled Hubbard junctions, but reduce rather than suppress AF order in $S$ = 3/2 or 2 junctions.

11 pages, 11 Figures and submitted to PRB

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Cited by in corpus (6)

• Spin-state ice in geometrically frustrated spin-crossover materials
• Chiral Y junction of quantum spin chains
• Boundary-induced spin density waves in linear Heisenberg antiferromagnetic spin chains with $\mathbf{S}\ge 1$
• A Study of Topological Quantum Phase Transition and Majorana Localization Length for the Interacting Helical Liquid System
• Tunneling density of states in a Y junction of Tomonaga-Luttinger liquid wires: A density matrix renormalization group study
• Enhancement in tunneling density of states in Luttinger liquid -- role of non-local interaction